Carbon nanotubes have been the subject of intense research since their discovery in 1991. Carbon nanotubes possess unique properties such as small size and electrical conductivity, which makes them suitable in a wide range of applications, including use as structural materials in molecular electronics, nanoelectronic components, and field emission displays. Carbon nanotubes may be multi-walled (MWNTs) or single-walled (SWNTs) and have dimensions in the nanometer range.
Depending on their atomic structure, carbon nanotubes may have metallic or semiconductor properties, and these properties, in combination with their small dimensions, make carbon nanotubes particularly attractive for use in fabrication of nano-devices. A major obstacle to such efforts has been the diversity of tube diameters, chiral angles, and aggregation states in nanotube samples obtained from the various preparation methods. Aggregation is particularly problematic because the highly polarizable, smooth-sided fullerene tubes readily form parallel bundles or ropes with a large van der Waals binding energy. This bundling perturbs the electronic structure of the tubes, and it confounds all attempts to separate the tubes by size or type or to use them as individual macromolecular species. The construction of nanotube-based electronic devices and the effort to fractionate nanotubes in order to obtain chirally pure fractions for specific electronic applications, however, requires such dispersion at the outset.
Of the methods used to disperse carbon nanotubes, sonication of carbon nanotube ropes in aqueous solutions of deoxyribonucleic acid (DNA) has been most successful (see commonly owned U.S. Ser. No. 10/716,346). While able to yield individually dispersed nanotubes that can subsequently be fractionated based on their electronic properties and diameter, the cost of doing so on a large scale is prohibitively expensive, owing primarily to the cost of the DNA. Small, inexpensive surfactants such as sodium dodecyl sulfate (SDS) have been used successfully for the dispersion but are not suitable for chromatographic fractionation based on electronic properties.
There remains a need therefore for inexpensive materials and methods for the dispersion of carbon nanotubes. Applicants have solved the stated problem by providing methods for the dispersion of carbon nanotubes using solutions of multiblock polymers.